Bug 1597068 - Revert navigator toolbox sheet anchor changes. r=dao

I'm not exactly sure what changed, but the changes from bug 149582 are no
longer needed to fix test_queryCaretRect.htm and the position of the
drop down dialog.

Differential Revision: https://phabricator.services.mozilla.com/D54066

--HG--
extra : moz-landing-system : lando

browser/themes/osx/browser.css

@@ -60,7 +60,8 @@
   content: "";
   display: -moz-box;
   -moz-appearance: toolbox;
-  height: 0;
+  height: 1px;
+  margin-top: -1px;
   opacity: 0.001;
 }